The invention relates to a device provided with a band-pass filter comprising two concentrically arranged coaxial resonator cavities and a coupling capacitor for mutually coupling the resonator cavities, the coupling capcitor comprising two plates and an intermediate dielectric body.
Such a device is inter alia used as an amplifier device for a TV transmitter, operating in the frequency range from 470-1000 MHz. The band-pass filter can be tuned by means of short-circuit plungers arranged in the resonator cavities to one of the channel frequencies in the UHF band.
One problem with such an arrangement is that the bandwidth of such a band-pass filter depends on the operating frequency. To avoid this, it is known to dimension during manufacture the amplifier device for a given TV channel by giving the dielectric body disposed between the capacitor plates a thickness which is specific for that channel frequency.
This has inter alia the drawback that a multichannel relay station must have a spare amplifier device for each TV channel and that preparing the coupling capacitor or, possibly, replacing this capacitor by another one is very elaborate and time-consuming.
It is an object of the invention to obviate these drawbacks in a very simple manner.